Acid recovery from acid-rich solutions

ABSTRACT

Provided is an unique, efficient and cost-effective process for the recovery of acid from acid-rich solutions. The process of the subject matter utilizes a strong oxidizer, such as Caro&#39;s acid, to disintegrate or render insoluble organic or inorganic materials such as carbohydrates and complexes thereof contained in acid-rich solutions, to make efficient and simple the separation and recovery of the acid solution. The acid recovered thus obtained is free of organic matter, and containing nearly all of the acid originally contained in the acid-rich solution.

TECHNOLOGICAL FIELD

The invention generally provides processes for recovery of acid fromacid-rich solutions and mixtures.

BACKGROUND

The regeneration of chemical-spent acid from industrial processes ishighly desirable for a verity of reasons, ranging from reducingindustrial waste and contamination of landfills to reduction of costsassociated with the reproduction of acid.

The recovery of acid has been demonstrated in a variety of industrialset-ups.

U.S. Pat. No. 2,631,974 [1] discloses an electrolytic system for therecovery of certain ingredients from the waste liquors discharged fromvarious chemical processes, in particular with the recovery of sulfateions in acid aqueous solutions containing them by the conversion thereofinto aqueous sulfuric acid solutions of sufficient purity to be ofcommercial value.

U.S. Pat. No. 8,052,953 [2] discloses a method for recovering sulfuricacid from concentrated acid hydrolysate of plant cellulose material.

One of the main barriers in utilizing acid in industrial applications isthe relatively high cost which is associated mainly with a high energyrequirement needed to recover it. Therefore, there is great need forreducing the production cost and energy requirements involved in suchprocesses.

Sulfuric acid is one of the more common acids in industrial use. Theaddition of hydrogen peroxide to sulfuric acid results in the formationof a very strong oxidizer, known as Caro's Acid or the Piranha solution,which has the ability to oxidize or hydroxylate most metal surfaces andremove most organic matter. The common application of the Piranhasolution is in the microelectronics industry to clean photoresistresidues from silicon wafers. It is also used to clean glassware byhydroxylating the surface, thus increasing the number of silanol groupson the surface.

U.S. Pat. No. 3,856,673 [3] discloses a process for purifying a spentacid stream containing organic impurities and at least 60% sulfuricacid. The process disclosed utilizes a stoichiometric amount of anoxidizer such as hydrogen peroxide to achieve oxidation of organicmaterials such as nitrocresols and nitrophenolic compounds.

Huling et al [4] teach oxidation of organic compounds utilizing hydrogenperoxide.

REFERENCES

-   [1] U.S. Pat. No. 2,631,974-   [2] U.S. Pat. No. 8,052,953-   [3] U.S. Pat. No. 3,856,673-   [4] Huling S. G. and Pivetz B. E. In Situ Chemical Oxidation.    Engineering Issue. Ground Water and Ecosystem Restoration    Information Center, UAEPA, EPA/600/R-06/072 (2006)

SUMMARY OF THE INVENTION

The inventors of the present invention have developed a unique,efficient and cost-effective process for the recovery of acid fromacid-rich solutions. The process of the invention utilizes a strongoxidizer, such as Caro's acid, to disintegrate or render insolubleorganic or inorganic materials such as carbohydrates and complexesthereof contained in acid-rich solutions, to thereby make efficient andsimple the separation and recovery of the acid solution. The acidrecovered is thus obtained as an aqueous acid solution, being free oforganic matter, and containing nearly all of the acid originallycontained in the acid-rich solution.

Thus, the invention described herein affords separating and recoveringacids, such as sulfuric acid, from a variety of organic components suchas hydrolysates of plant cellulose materials commonly used in the paperindustry, such components may or may not be “in solution”, namely someor all of the organic components may be insoluble in the originalacid-rich solution to be recovered.

In one of its aspects, the present invention provides a process for acidrecovery from an acid-rich aqueous solution, the solution comprising atleast one acid to be recovered and at least one organic material (beingdifferent from the acid material and typically containing at least onecarbohydrate material or a complex thereof), the process comprising:

-   -   treating said solution with at least one oxidizer or at least        one precursor of the oxidizer, wherein the oxidizer is capable        of oxidizing the organic material contained in the solution into        at least one insoluble or gaseous species;    -   removing or allowing separation of said insoluble or gaseous        species from the acid solution;

to yield a substantially enriched acid solution, substantially free oforganic matter (being free of said organic impurities, as disclosedherein).

The invention further provides a process for recovery of acid, such assulfuric acid, from an acid-rich mixture comprising at least one acid,e.g., sulfuric acid, and an amount of organic matter, the processcomprising contacting the mixture with an oxidizer or a precursorthereof, thus producing an acid enriched solution, wherein the oxidizedorganic matter precipitates or evaporates from the acid enrichedmixture.

The enriched acid solution being substantially free of organic mattermay be further treated to further remove traces of unoxidized organicmatter, residues of oxidized organic matter and insoluble species.

In some embodiments, the enriched acid solution being substantially freeof organic matter contains up to 1,000 ppm of organic matter.

The acid solution may be any acid-containing aqueous solution which isused or generated in any one of a variety of industries or industrialprocesses, ranging from stainless steel production to microchipmanufacturing. As the acid content may vary based on the industry or theprocess producing the acid waste, the process of the invention may besuitably configured and adapted to achieve full recovery of the acid.

In accordance with the invention, the oxidizer or a precursor thereof(e.g., hydrogen peroxide) is added to the acid-rich solution at roomtemperature. The reaction mixture comprising the acid-rich solution andthe oxidizer or precursor thereof may be allowed to react over a periodof between 1 hours and 7 days at room temperature (25-30° C.), at atemperature above 50° C., or at a temperature above 60° C., or at atemperature above 70° C., or at a temperature above 80° C., or at atemperature above 90° C., or at a temperature above 100° C., or at atemperature above 110° C., or at a temperature above 120° C., or at atemperature above 130° C., or at a temperature above 140° C., or at atemperature above 150° C., or at a temperature between 50° C. and 100°,or at a temperature between 60° C. and 110°, or at a temperature between70° C. and 120°, or at a temperature between 80° C. and 130°, or at atemperature between 90° C. and 140°, or at a temperature between 100° C.and 150°, or at a temperature between 50° C. and 150°, or at atemperature between 60° C. and 140°, or at a temperature between 70° C.and 130°, or at a temperature between 80° C. and 120°, or at atemperature between 90° C. and 100° C.

In accordance with the invention, the oxidizer or a precursor thereof(e.g., hydrogen peroxide) is added to the acid-rich solution at atemperature below room temperature (being the temperature at which thereaction mixture comprising the acid-rich solution and the oxidizer orprecursor thereof may be allowed to react). In some embodiments, thetemperature is between −30° C. (minus 30 degrees Centigrade) and 0° C.In some embodiments, the temperature is between −30° C. and −20° C. Insome embodiments, the temperature is between −30° C. and −10° C. In someembodiments, the temperature is between −20° C. and −10° C. In someembodiments, the temperature is between −20° C. and 0° C. In someembodiments, the temperature is between −10° C. and 0° C. In someembodiments, the temperature is between −30° C. and 5° C. In someembodiments, the temperature is between −30° C. and 10° C. In someembodiments, the temperature is between −30° C. and 15° C. In someembodiments, the temperature is between −30° C. and 20° C. In someembodiments, the temperature is between −30° C. and 25° C. In someembodiments, the temperature is between −30° C. and 30° C. In someembodiments, the temperature is between 0° C. and 5° C. In someembodiments, the temperature is between 0° C. and 10° C. In someembodiments, the temperature is between 0° C. and 15° C. In someembodiments, the temperature is between 0° C. and 20° C. In someembodiments, the temperature is between 0° C. and 25° C. In someembodiments, the temperature is between 0° C. and 30° C.

In some cases, the oxidizer or a precursor thereof is added to theacid-rich solution at room temperature and the temperature of thereaction mixture is allowed to increase spontaneously (in case of anexothermic reaction). In some embodiments, the temperature increase iscontrolled such that the temperature does not increase above 50° C.,above 60° C., above 70° C., above 80° C., above 90° C., above 100° C.,above 110° C., above 120° C., above 130° C., above 140° C., or to above150° C.

After the oxidizer completely oxidizes the organic material, traces ofthe organic material and the remaining oxidizing agents may be removedfrom the acid enriched solution using any method that is common in thefield of the art. In some embodiments, the solid oxidized material andsolid oxidizer may be removed by filtration. Where the oxidized materialis a gaseous species, it may be removed from the acid-enriched solutionby evaporation, by heating, under vacuum, by stirring, or by saturatingthe acid-enriched solution with an inert gas.

In some embodiments, the trace materials and the remaining oxidizingagents may be removed by mechanical or chemical adsorption or byabsorption e.g., on activated carbon, by flocculation or precipitation.

The process of the invention may be repeated by employing consecutivecycles and using the herein defined substantially carbon-free acidformulation as a substrate in acid-based processes.

The oxidizer used in accordance with the invention is typically a“strong oxidizer” which is capable of converting an organic materialinto one or more oxide forms which are less soluble or more easilyevaporable as compared to the unoxidized form. The oxidizer is said ofbeing a strong oxidizer as it is capable of oxidizing the majority ofthe organic material contained in the solution, namely 100 wt % of theorganic material, 99%, 98%, 97%, 96%, 95%, 94%, 93%, 92%, 91%, 90%,between 80% and 100%, between 90% and 100%, between 80% and 95%, orbetween 80% and 90% of the organic material. Typically, the oxidizedform of the organic material is insoluble in the acid solution or iseasily removable from the acid solution, e.g., by evaporation, byfiltration, by heating, under vacuum, by activated carbon, etc.

In some embodiments, the oxidizer has a Standard ElectrodePotentials)(E° greater than +1 Volts.

In some embodiments, the oxidizer is selected to have E° between +1 and+2. The oxidizer is selected to effectively oxidize the organic materialwithout substantially chemically affecting the acid component. Somenon-limiting examples of oxidizers include ammonium perchlorate,ammonium permanganate, barium peroxide, bromine, calcium chlorate,calcium hypochlorite, chlorine trifluoride, chromium anhydride, chromicacid, dibenzoyl peroxide, fluorine, hydrogen peroxide, magnesiumperoxide, nitrogen trioxide, perchloric acid, potassium bromated,potassium chlorate, potassium peroxide, propyl nitrate, sodium chlorate,sodium chlorite, sodium perchlorate, sulphuric acid and sodium peroxide.

In some embodiments, the oxidizer is hydrogen peroxide (H₂O₂).

In other embodiments, the oxidizer is H₂SO₅ (Caro's acid). In someembodiments, H₂SO₅ (Caro's acid) is formed in situ.

In some embodiments, the oxidizer is utilized for forming in situ astronger oxidizer.

According to embodiments where the oxidizer is formed in situ, anoxidizer (e.g., hydrogen peroxide) or a precursor of the oxidizer whichis convertible into the oxidizer in the presence of the acid in theacid-rich solution, is added to the acid-rich solution and transforms anamount of the acid in the solution into the oxidizer. In embodimentswhere a precursor of the strong oxidizer is hydrogen peroxide and theacid is sulfuric acid, a small amount of “Caro's acid” forms in situ andoxidizes the carbon-based or carbon-containing material, e.g.,carbohydrates, to at least one insoluble or gaseous species (e.g., CO₂and SO₂) and water; thus, yielding a substantially carbon-free acidenriched solution (e.g., sulfuric acid).

Thus, the invention also contemplates a process for acid recovery froman acid-rich aqueous solution, the solution comprising at least oneorganic material (being different from the acid material and selected,e.g., from carbohydrates and complexes thereof), the process comprising:

-   -   treating said solution with Caro's acid or with at least one        precursor thereof for enabling in situ formation of Caro's acid        in the solution, wherein the organic material contained in the        solution is transformed into at least one insoluble or gaseous        species;    -   removing or allowing separation of said insoluble or gaseous        species from the acid solution;

to yield a substantially enriched acid solution, substantially free oforganic matter.

As noted above, where Caro's acid is used in the process of theinvention, the acid-rich solution may be treated with an amount of apre-prepared Caro's acid or may be treated with an amount of sulfuricacid and hydrogen peroxide, step wise, to form in situ the Caro's acidand permit transformation of the organic material, as detailed herein.

The invention further provides a process for recovery of sulfuric acidfrom an aqueous solution rich in sulfuric acid, the solution furthercomprising at least one soluble organic material, as defined herein, theprocess comprising:

-   -   treating said solution with Caro's acid or with hydrogen        peroxide, to transform the organic material contained in the        solution into at least one insoluble or gaseous species;    -   removing or allowing separation of said insoluble or gaseous        species from the acid solution;

to yield a substantially enriched acid solution, substantially free oforganic matter.

The “acid rich solution” is generally a formulation or a combination ofmaterials or a mixture or a medium comprising between about 5% andbetween about 98% acid by weight, water and at least one carbonmaterial. The acid in the acid-rich solution may be an organic ormineral acid. In some embodiments, the solution comprises between about5% and about 90% acid by weight, or between about 30% and about 85% acidby weight, or between about 30% and about 80% acid by weight, or betweenabout 30% and about 75% acid by weight, or between about 30% and about60% acid by weight.

In some embodiments, the solution comprises between about 35% and about95% acid by weight, or between about 40% and about 95% acid by weight,or between about 45% and about 95% acid by weight, or between about 50%and about 95% acid by weight, or between about 55% and about 95% acid byweight.

In some embodiments, the solution comprises between about 40% and about90% acid by weight, or between about 50% and about 85% acid by weight,or between about 60% and about 80% acid by weight, or between about 60%and about 75% acid by weight, or between about 60% and about 65% acid byweight.

In some embodiments, the solution comprises between about 60% and about90% acid by weight, or between about 60% and about 85% acid by weight,or between about 60% and about 80% acid by weight, or between about 60%and about 75% acid by weight, or between about 60% and about 65% acid byweight, or between about 70% and about 90% acid by weight, or betweenabout 70% and about 85% acid by weight, or between about 70% and about80% acid by weight, or between about 70% and about 75% acid by weight,or between about 80% and about 95% acid by weight, or between about 80%and about 90% acid by weight, or between about 80% and about 85% acid byweight, or between about 90% and about 95% acid by weight.

In some embodiments, the concentration of the acid in the acid-richsolution is between 1 and 98%, or between 30% and 63%. In otherembodiments, the concentration of the acid is between 40% and 63%,between 59% and 63% or is between 60 and 64%.

The acid to be recovered from the acid-rich solution may be a singletype of acid or a combination of acids. The acid is usually recovered asan aqueous solution.

As the process of the invention permits conversion of the organicsoluble and insoluble materials contained in the acid-rich solution intoinsoluble organic materials or gaseous species, and permitting theirremoval, without substantially affecting the acid content, the processof the invention is suited for recovering a plurality of acids and acidcombinations. In some embodiments, the acid to be recovered is a mineralacid. Some non-limiting examples of mineral acids include hydrochloricacid (HCl), nitric acid (HNO₃), phosphoric acid (H₃PO₄), sulfuric acid(H₂SO₄), boric acid (H₃BO₃), hydrofluoric acid (HF), hydrobromic acid(HBr) and perchloric acid (HClO₄).

In some embodiments, the acid is sulfuric acid (H₂SO₄). In someembodiments, the acid-rich solution containing sulfuric acid is treatedwith a precursor of a strong oxidizer capable of reacting with an amountof the sulfuric acid in the solution to form a strong oxidizer. In someembodiments, the precursor is hydrogen peroxide.

As stated above, the majority of the organic material contained in theacid-rich solution is removed. Thus, the resulting substantiallycarbon-free acid solution contains an aqueous acid (e.g. sulfuric acid)solution that contains less than 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%,1%, 0.5%, 0.3%, 0.1% by weight of a carbon material.

The amount of the organic material remaining after acid recovery, namelythe Total Organic Carbon (TOC) may be determined by a variety ofmethods, for example: (1) TOC Analyzer, and (2) titration withanalytical KMnO₄.

In some embodiments, the TOC may be measured in parts per million (ppm).In such embodiments, the resulting substantially carbon-free acidsolution contains between 0.05 and 900 ppm TOC. In some embodiments, theamount of TOC is between 5 and 900 ppm, between 5 and 500 ppm, between 5and 300 ppm, between 10 and 900 ppm, between 10 and 500 ppm, between 10and 300 ppm, between 50 and 900 ppm, between 50 and 500 ppm, between 50and 300 ppm, between 100 and 900 ppm, between 100 and 500 ppm, between100 and 300 ppm, between 500 and 1,000 ppm, between 600 and 1,000 ppm,between 700 and 1,000 ppm, between 800 and 1,000 ppm or between 900 and1,000 ppm.

The carbon material may be any carbonaceous material, i.e., any materialcontaining or composing carbon. The carbonaceous material may be of highmolecular weight.

The “organic material”, or “organic matter”, or “carbon materials”, allbeing used herein interchangeably, is “carbonaceous material”, based oncarbon and may or may not be soluble in the acid solution. In someembodiments, the organic matter is insoluble in the acid solution. Insome embodiments, the organic matter is fully soluble in the acidsolution. In some embodiments, the organic matter is a mixture of suchmaterials, some are soluble and the remaining insoluble in the acidsolution. In some embodiments, the organic matter comprises at least 50%insoluble material (in the acid solution). In some embodiments, theorganic matter comprises a mixture of soluble and insoluble materials,present in a ratio of 0.001:99.999, respectively (out of the totalamount, weight, of the organic matter to be oxidized and removed). Insome embodiments, the w/w ratio is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7,1:8, 1:9, 1:10, 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 2:3, 2:5,2:7, 2:9, 2:11, 11:2, 9:2, 7:2, 5:2, 3:2, respectively.

The organic material may be selected from biological materials, organicmaterials derived from nature, solvents, and/or organic chemicals usedin various industries. In some embodiments, the organic material isselected from natural materials such as hydrocarbons, carbohydrates,proteins, amino acids, lignin, lipid and natural resins. In someembodiments, the carbonaceous material is at least one carbohydratematerial.

In some embodiments, the organic material to be oxidized and therebyremoved is at least one hydrolysate of plant cellulose material, e.g.,as commonly used in the paper industry. In some embodiments, the organicmaterial to be oxidized and thereby removed is at least one carbohydrateor a complex thereof. In some embodiments, the organic material to beoxidized and thereby removed is at least one carbohydrate decompositionproduct, such as furfural, levulinic acid, hydroxymethylfurfural (HMF),acetic acid, formic acid, monosaccharides such as glucose and xylose andothers.

For example, sulfuric acid-containing waste solutions are products of agreat variety of processes used in the biomass industry where biomass,such as wood or wood products, is treated with acid to separate outvarious hydrocarbons, particularly carbohydrates. Cellulose which makesup the major part of plant biomass is greatly used in a variety ofindustries, particularly in the paper industry, e.g., acid-richsolutions of hydrolyzed cellulose products.

Nano Crystalline Cellulose (NCC) also known as Cellulose Whiskers (CW)and crystalline nanocellulose (CNC), are fibers produced from acidhydrolysis of cellulose, typically being high-purity single crystals ofcellulose. Thus, in such processes for the production of NCC largeamounts of acid, e.g., sulfuric acid, are used, which may be regeneratedas disclosed herein.

Thus, the herein defined acid-rich solution may be a byproduct of aprocess of NCC production or a byproduct of any chemical process whichyields the herein defined acid-rich solution. Thus, in some embodiments,the carbon material is a hemicellulose derivative. In some embodiments,the carbon material is selected from galactose, rhamnose, arabinose,xylose, mannose, cellulose, glucose, hydroxymethylfurfural (HMF),galacturonic acid, lignin derivatives, levulinic acid, cellulose ethersand cellulose esters.

In some embodiments, the carbon material is a carbohydrate, adisaccharide, a monosaccharide, an oligosaccharide or a polysaccharide.

In some embodiments, the concentration of the acid (e.g., sulfuric acid)in the NCC acid-rich solution comprising acid and a carbohydrate isbetween 1 and 98%, or between 30% and 63%. In other embodiments, theconcentration of the acid is between 40% and 63%, between 59% and 63% oris between 60 and 64%.

Thus, the process of the invention may be utilized to purify and collectacid-rich solutions used in the paper industries and may comprise atleast one carbohydrate as defined herein, or at least one hemicelluloseor derivative thereof, or any of the carbonaceous materials disclosed.

The amount of oxidizer precursor (e.g., hydrogen peroxide) to be added,according to some embodiments, to the acid-rich formulation for enablingin situ synthesis of the strong oxidizer (e.g., Caro's acid) depends ofvarious parameters inter alia reaction time, temperature, carbohydrateconcentration, acid:solid ratio, as recognized by the person of skill inthe art. In some embodiments, the precursor, e.g., hydrogen peroxide, isadded to the acid-rich formulation at a concentration of between about 2and about 10%. In other embodiments, the amount of the precursormaterial, e.g., hydrogen peroxide is between 2 and 9%, between 2 and 8%,between 2 and 7%, between 2 and 6%, between 2 and 5%, between 2 and 4%,between 2 and 3%, between 3 and 10%, between 3 and 9%, between 3 and 8%,between 3 and 7%, between 3 and 6%, between 3 and 5%, between 3 and 4%,between 4 and 10%, between 4 and 9%, between 4 and 8%, between 4 and 7%,between 4 and 6%, between 4 and 5%, between 5 and 10%, between 5 and 9%,between 5 and 8%, between 5 and 7%, between 5 and 6%, between 6 and 10%,between 6 and 9%, between 6 and 8%, between 6 and 7%, between 7 and 10%,between 8 and 10%, or between 9 and 10%.

In other embodiments, the amount of precursor material, e.g., hydrogenperoxide, is between 10 and 30%, between 12 and 30%, between 14 and 30%,between 16 and 30%, between 18 and 30%, between 20 and 30%, between 22and 30%, between 24 and 30%, between 26 and 30%, between 28 and 30%,between 10 and 25%, between 12 and 25%, between 14 and 25%, between 16and 25%, between 18 and 25%, between 20 and 25%, between 10 and 20%,between 12 and 20%, between 14 and 20%, between 16 and 20%, between 18and 20%, between 25 and 30%, between 3 and 30%, between 5 and 30%,between 7 and 30% or between 9 and 30%.

In some embodiments, the amount of the precursor material e.g., hydrogenperoxide, or the amount of the oxidizer is not stoichiometric.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosedherein and to exemplify how it may be carried out in practice,embodiments will now be described, by way of non-limiting example only,with reference to the accompanying drawings, in which:

FIGS. 1A-C provide a general depiction of carbohydrate decomposition inthe presence of a strong oxidizer.

FIG. 1A depicts the carbohydrates produced following hydrolysis ofcellulose.

FIG. 1B shows the general decomposition process of carbohydrates.

FIG. 1C shows a suggested mechanism for the oxidation of carbohydratesby H₂SO₅ (Caro's acid).

FIG. 2 shows the oxidation reaction progress monitored by colorimetricanalysis using 5% H₂O₂.

FIGS. 3A-B shows the absorbance vs. oxidation time using 3% H₂O₂ (FIG.3A) and 7.5% H₂O₂ (FIG. 3B) for 0-19 days.

FIG. 4 depicts an example for adsorption of the remaining organic tracesand oxidizing agents in the solution using activated carbon.

FIG. 5 describes adsorption of the remaining organic traces andoxidizing agents in the solution using activated carbon over time.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention provides a process for separating or recovering acid fromacid-rich solutions comprising soluble and/or insoluble organic matter.The cost-effectiveness of the process of the present invention isimproved considerably compared to prior art processes as a result ofusing an oxidizer which is capable of substantially completely oxidizingthe organic material while leaving unaffected the acid material, thusnot affecting acid losses. Under such a set up, it is possible to carryout the acid recovery at a relatively low temperature, e.g., below 100°C., and from acid solutions containing no less than between 100 and 400times as much organic contaminants.

An additional advantage of the invention resides in the fact that no, oronly little, undesired by-products, such as soluble oxidized organicmaterials are formed. These too may be removed by further processing ofthe acid solution.

Example 1: Process of Recovering Acid from Acid-Rich Formulations

7.54 kg of 30% H₂O₂ (5% of H₂O₂ weight per weight final solution) wereloaded at R.T to 38 kg ˜60% sulfuric acid suspension containing 2.2%carbohydrates (weight per solution weight). The composition of thesuspension was around 2/3 of insoluble complex carbohydrates (e.g.cellulose, hemicellulose) and ⅓ soluble carbohydrates(monomeric+polymeric) and their derivatives. Such an acid formulationcontained glucose (9.8 g/L-30 g/L), galactose (<0.2 g/L), arabinose(<0.2 g/L), mannose (<0.2 g/L), xylose (0.6 g/L-1.8 g/L), formic acid(<1 g/L), acetic acid (<1 g/L), levulinic acid (<1 g/L),hydroxymethylfurfural (HMF) (<0.2 g/L) and furfural (<0.2 g/L).

The reaction mixture was stirred at R.T until it exothermed or wasrefluxed)(110°-130° and monitored by spectrophotometer. After 90 minutesthe absorption in the region 400 nm-1100 nm reached a minimum,indicating that the majority of the organic material was oxidized.Thereafter, the reaction was cooled down. After 90 minutes, the solutionwas completely clear.

The thus-obtained cleared acid formulation was basically free of organicmatter, or contained very minute amounts of organic matter. To furtherpurify the acid formulation, the following steps were optionally carriedout.

0.76 kg of activated carbon (2% of Activated carbon weight per weight ofinitial 60% acid) were loaded at R.T to a “cleared solution” of 44 kg˜50% sulfuric acid solution containing traces of carbohydrates and ˜5%H₂O₂. The solution was mixed and monitored by spectrophotometer and TOClevels measured by titration with KMnO₄. After 8 h the absorption in theregion 400 nm-1100 nm and the titer amount reached minimum and thereaction was cooled down and filtered. The “cleaned solution” wasthereafter used in further acid-based reactions.

Example 2: General Process of Recovering Acid from Acid-RichFormulations from NCC Production Processes

The above process was also used for acid recovery of acid formulationsused in industrial process for utilizing paper products, paper pulp orgenerally cellulose materials.

The general sequence of process steps is exemplifies herein by acidrecovery from an acid-rich solution which is an end-solution in theproduction of NCC. The process of the invention may comprise:

-   -   Step 1. Separation of concentrated sulfuric acid from the        hydrolyzed NCC suspension; and    -   Step 2. Decomposition of carbohydrates contained in the sulfuric        acid solution by the addition of hydrogen peroxide.        The oxidized products may thereafter be removed by a multitude        of additional steps or ways.

The process of the present invention may further comprise additionalsteps as follows:

-   -   Step 1. Separation of concentrated sulfuric acid from the        hydrolyzed NCC suspension;    -   Step 2. Decomposition of carbohydrates contained in the sulfuric        acid solution by the addition of hydrogen peroxide;    -   Step 3. Decomposition of the remaining oxidizing agents by        different methods such as UV, activated carbon etc.; and    -   Step 4. Optionally, adsorption of the remaining organic traces        in the solution using an adsorbent such as activated carbon.

In a process conducted according to the invention, implementing steps 1,2 and optionally steps 3 and 4, and in order to maximize recovery of thesulfuric acid, a controlled hydrolysis of cellulose fibers was furthercarried out.

The conditions for the acid hydrolysis used to extract the crystallineparticles from a variety of cellulose sources was very narrow (e.g.,acid concentration, reaction time, temperature, acid:solid ratio). It iscommonly known that during at the end of the hydrolysis, during NCCproduction, the mixture is typically diluted with water to quench thereaction, and only then the mixture undergoes a series of separation andwashing (centrifugation or filtration). The more the acid is diluted,the less cost effective its recovery. Thus, the present inventionrenders such dilution steps unnecessary, and thus cost-effective.

Example 3: Process of Recovering Acid from Acid-Rich Formulations fromNCC Production Processes Step 1: Separation of Concentrated Acid

Following separation of concentrated sulfuric acid from the hydrolyzedNCC suspension, the high majority of the reaction mixture weight wasobtained in the supernatant in the first separation. This “usedsolution” contained nearly all of the acid originally used in thereaction for making the NCC, along with soluble carbohydrates.

The NCC was precipitated with some of the acid originally put in.

Step 2: Decomposition of Carbohydrates in Sulfuric Acid Solution byHydrogen Peroxide

The “used solution” contained a variety of carbohydrates. Thecomposition of the “used solution” depended on the cellulosic rawmaterial and on the hydrolysis conditions. FIG. 1A shows thecarbohydrates produced from the hydrolysis of cellulose. For a solutionthat also contained other saccharides such as xylose, mannose and otherhemicellulose derivatives, similar products were depicted. FIG. 1B showsthe general decomposition process of the carbohydrates.

The addition of hydrogen peroxide to sulfuric acid results in theformation of Caro's Acid or Piranha solution. A suggested mechanism forthe oxidation of the carbohydrates by Caro's acid is provided in FIG. 1Cwhich demonstrates how the organic matter is converted to carbondioxide.

7.54 kg of 30% H₂O₂ (5% of H₂O₂ weight per weight final solution) wereloaded at R.T to a “used solution” of 38 kg ˜60% sulfuric acid solutioncontaining 2.6% carbohydrates (weight per solution weight). Theoxidation reaction of the sulfuric acid solution was carried out fivedays after separation of the hydrolysis mixture (step 1). The reactionmixture was then refluxed)(110°-130° and monitored by spectrophotometer.After 90 minutes the absorption in the region 400 nm-1100 nm reached aminimum (FIG. 2), indicating that the majority of the organic materialwas oxidized. Thereafter, the reaction was cooled down. The colorreduction could be seen with time. After 90 minutes, the solution wascompletely clear.

As FIGS. 3A-B show, for a given carbohydrate concentration, the optimaloxidation time was 90 minutes up to 6 days from the day of hydrolysisand first separation (i.e., step 1). Prolonged periods required longeroxidation times. However, complete oxidation and full recovery of acidwas always possible. The optimal minimum percentage of hydrogen peroxiderequired for oxidizing the organic matter, depended on the carbohydrateconcentration in the sulfuric acid solution. FIG. 4 shows that for a2.6% concentration, 5% H₂O₂ was optimal for some solutions since itenabled the same performance of 7.5% with less dilution of the acid.

Step 3 (and Step 4): Adsorption of the Remaining Organic Traces andOxidizing Agents in the Solution Using Activated Carbon.

This optional step(s) in the recovery process has two objectives:

A. Removal of organic traces that remained after step 2;

B. Removal of oxidizer.

0.76 kg of activated carbon (2% of Activated carbon weight per weight ofinitial 60% acid) were loaded at R.T to a “cleared solution” of 44 kg˜50% sulfuric acid solution containing traces of carbohydrates and ˜5%H₂O₂. The solution was mixed and monitored by spectrophotometer and TOClevels measured by titration with KMnO₄. After 8 h the absorption in theregion 400 nm-1100 nm and the titer amount reached minimum (FIG. 5) andthe reaction was cooled down and filtered. The “cleaned solution” wasthereafter used in further acid-based reactions.

1.-40. (canceled)
 41. A process for acid recovery from an acid-richaqueous solution, the solution comprising at least one organic material,the process comprising: treating said solution with Caro's acid or withat least one precursor thereof for enabling in situ formation of Caro'sacid in the solution, wherein the organic material contained in thesolution is transformed into at least one insoluble or gaseous species;removing or allowing separation of said insoluble or gaseous speciesfrom the acid solution; to yield a substantially enriched acid solutionbeing substantially free of organic matter.
 42. The process according toclaim 41, wherein the acid-rich solution is treated with an amount of apre-prepared Caro's acid.
 43. The process according to claim 41, whereinthe acid-rich solution is treated with an amount of sulfuric acid andhydrogen peroxide, to form Caro's acid in situ.
 44. The processaccording to claim 41, wherein the acid in the acid-rich solution is amineral acid.
 45. The process according to claim 41, wherein thesolution comprises between about 30% and about 60% acid by weight, waterand at least one organic material.
 46. The process according to claim41, wherein the acid to be recovered from the acid-rich solution isselected from the group consisting of hydrochloric acid (HCl), nitricacid (HNO₃), phosphoric acid (H₃PO₄), sulfuric acid (H₂SO₄), boric acid(H₃BO₃), hydrofluoric acid (HF), hydrobromic acid (HBr) and perchloricacid (HClO₄).
 47. The process according to claim 46, wherein the acid issulfuric acid.
 48. The process according to claim 47, wherein theacid-rich solution containing sulfuric acid is treated with a precursorof an oxidizer capable of reacting with an amount of the sulfuric acidin the solution to form the oxidizer.
 49. The process according to claim48, wherein the precursor is hydrogen peroxide.
 50. The processaccording to claim 41, wherein the amount of the oxidizer precursoradded to the acid-rich solution for enabling in situ formation of theoxidizer is between about 2 and about 6%.
 51. A process for recovery ofsulfuric acid from an aqueous solution rich in sulfuric acid, thesolution further comprising at least one organic material, the processcomprising: treating said solution with Caro's acid or with hydrogenperoxide, to transform the organic material contained in the solutioninto at least one insoluble or gaseous species; removing or allowingseparation of said insoluble or gaseous species from the acid solution;to yield a substantially enriched acid solution being substantially freeof organic matter.
 52. The process according to claim 41, wherein the atleast one organic material comprises soluble and insoluble organicmaterial.
 53. The process according to claim 52, wherein the at leastone organic material is fully solubilized in the acid-rich solution. 54.The process according to claim 52, wherein the at least one organicmaterial is a mixture of soluble and insoluble organic materials. 55.The process according to claim 52, wherein the at least one organicmaterial is insoluble in the acid-rich solution.
 56. Recovered acidsolution comprising water and at least one acid, optionally furthercomprising up to 1,000 ppm organic matter, the solution obtainable bythe recovery process of claim
 41. 57. The solution according to claim56, wherein the acid is sulfuric acid.